Loose ends on cigarettes are a source of dissatisfaction and complaints from smokers. A "loose end" is an end of a cigarette which is insufficiently filled with tobacco. When the tobacco in the end of a cigarette is too loosely packed or has too low a packing density, tobacco particles and shreds can fall out of the end of the cigarette as it is removed from the pack. Moreover, a cigarette having a loose end can be difficult to light uniformly and the burning of the cigarette, at least during the initial puffs, may not be uniform. Cigarettes therefore undergo one or more tests during the manufacturing process in order to identify and reject cigarettes having loose ends.
A variety of techniques have been used to identify loose ends on cigarettes. Manually, in an off line method, cigarettes can be examined by an expert viewing the ends of the cigarette along their longitudinal axis. Automated techniques include mechanical testing such as pin insertion into the cigarette end optical testing where special optics are used to view and examine the end of a cigarette; and electrical techniques for examining the electrical properties of the cigarette end.
For example, U.S. Pat. No. 3,368,674 to Koeppe describes a method and apparatus for testing the ends of cigarettes by inserting a pin into the end of a cigarette. If the end is too soft, the pin extends excessively into the cigarette end. The pin insertion method has inherent mechanical limitations and cannot, for example, be used in conjunction with modern, high speed cigarette manufacturing operations.
A more recent method and apparatus for testing the end portions of cigarettes is described in U.S. Pat. No. 3,993,194. This apparatus, which is employed commercially in the industry involves capacitive sensing of the density at the end of the cigarette. The end of the cigarette is passed in close proximity to the electrodes of a capacitor. The change in the electric field is measured to provide an indication of the tobacco density at the end of the cigarette. Such capacitive inspection of cigarettes can be conducted at high speeds. But this testing method can be influenced by various extraneous factors such as relative humidity in the manufacturing environment, varying amounts of moisture in the tobacco, and/or differing types of tobaccos in the tobacco blend, leading to inaccuracies in the proper identification of cigarettes having loose ends.
U.S. Pat. No. 4,496,055 to Green et al. describes an optical method for identifying cigarettes having loose ends. Cigarettes are passed through a channel including a pair of photoelectric cells which direct light, preferably of the infrared spectrum, radially inwardly into the tobacco tip of the cigarette. A fiber optic detector perpendicular to the end of the cigarette measures the infrared light reflected from the end of the cigarette along its longitudinal axis to thereby distinguish between cigarettes having ends properly filled with tobacco and those having ends insufficiently filled with tobacco. The insufficiently filled cigarettes are rejected. In this device, the distance between the end of the cigarette and the fiber optic detector is an important parameter and a potential source of inaccuracy. Similarly, cigarettes having a loose end portion but with substantial amounts of tobacco shreds at only the end, per se, of the cigarette, may not be identified as defective.
The above and other processes and apparatus have been and are used commercially to test the tobacco ends of cigarettes as they are conveyed serially during the manufacturing process. Because of various difficulties such as those identified above, and others, none of the commercially available on-line systems for detecting loose ends have proven to be satisfactorily accurate and reliable over the long term in the manufacturing environment. For example, with some systems cigarettes having loose ends are not properly identified and rejected. With other systems, properly manufactured cigarettes, having satisfactorily filled ends are nevertheless rejected. Some systems suffer both such shortcomings.
In most cigarette manufacturing processes, loose end inspection is conducted at at least two locations. The first inspection is conducted on individual cigarettes, just after their manufacture. The cigarettes are thereafter inspected downstream, as a group, during the packaging or packing operation where groups of typically, 20, cigarettes are packed into a package. A single cigarette having a loose end when identified first at the packing stage of manufacture, results in the rejection of an entire cigarette package, thus causing the rejection of 19 satisfactory cigarettes along with the 1 defective cigarette. In addition to waste of satisfactory cigarettes, this results in waste of satisfactory packaging materials.
As cigarette manufacturing speeds have increased from several thousand cigarettes per minute to 8,000 or more cigarettes per minute, the accuracy of tobacco end inspection systems has decreased. Thus, despite the continual and well recognized need for improved cigarette end inspection systems, and despite continuing efforts to improve these systems, there is still no commercially available inspection system which has been found to be both highly accurate and reliable in the manufacturing environment.